Northern wintertime atmospheric fluctuations on very large (near global) spatial scales and monthly to seasonal temporal scales are associated with geographically-fixed standing oscillations with large wavelike structure. One such pattern which often influences the seasonal character over the U.S. is referred to as the PNA pattern because of clear connections between atmospheric states over the near-equatorial Pacific Ocean and North America. This pattern (called PNA teleconnection pattern) is often enhanced during warming events (El Nino/Southern Oscillation episodes) in the equatorial Pacific Ocean. While the spatial pattern is well known, its time behavior, including onset, maturity, and decay, are not yet understood. These properties are important to understanding the dynamical nature of intra-seasonal variability and to developing numerical methods for their prediction. The PIs, Drs. Wallace and Kushnir are proposing to carry out systematic diagnostic studies of the temporal behavior of such teleconnection patterns. The proposal concerns the study of atmospheric teleconnection patterns on time scales of 30-150 days. The analysis emphasizes a comparison between the observations and general circulation model data from the NCAR CCM. The 30-150 day fluctuations will be isolated in the data using digital filtering. The patterns will be identified using a rotated principal component analysis. The goals of the study are: (a)To determine the characteristics of the temporal evolution of the patterns (b)To identify the changes in the circulation during periods of onset and decay of the patterns.
